1. Field of the Invention
The disclosure relates generally to methods and apparatus for dispensing a viscous material on a substrate, such as a printed circuit board.
2. Discussion of Related Art
There are several types of prior art dispensing systems used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is the assembly of integrated circuit chips and other electronic components onto circuit board substrates. In this application, automated dispensing systems are used for dispensing dots of liquid epoxy or solder paste, or some other related material, onto circuit boards. Automated dispensing systems are also used for dispensing lines of underfill materials and encapsulents, which mechanically secure components to the circuit board. Underfill materials and encapsulents are used to improve the mechanical and environmental characteristics of the assembly.
Another application is to dispense very small amounts or dots onto a circuit board. In one system capable of dispensing dots of material, a dispenser unit utilizes a rotating auger having a helical groove to force material out of a nozzle and onto a circuit board. One such system is disclosed in U.S. Pat. No. 5,819,983, entitled LIQUID DISPENSING SYSTEM WITH SEALING AUGERING SCREW AND METHOD FOR DISPENSING, which is owned by Speedline Technologies, Inc. of Franklin, Mass., the assignee of the disclosure.
In an operation employing an auger-type dispenser, the dispenser unit is lowered towards the surface of the circuit board prior to dispensing a dot or a line of material onto the circuit board and raised after dispensing the dot or line of material. Using this type of dispenser, small, precise quantities of material may be placed with great accuracy. The time required to lower and raise the dispenser unit in a direction normal to the circuit board, typically known as a z-axis movement, can contribute to the time required to perform dispensing operations. Specifically, with auger-type dispensers, prior to dispensing the dot or line of material, the dispenser unit is lowered so that the material touches or “wets” the circuit board. The process of wetting contributes to additional time to perform the dispensing operation.
It is also known in the field of automated dispensers to stream viscous material on the circuit board. Such a system is shown and described in U.S. patent application Ser. No. 11/707,620, filed Feb. 16, 2007, entitled METHOD AND APPARATUS FOR DISPENSING A VISCOUS MATERIAL ON A SUBSTRATE, which claims priority to U.S. Provisional Patent Application No. 60/856,508, filed Nov. 3, 2006, both of which are owned by Speedline Technologies, Inc. of Franklin, Mass. and incorporated herein by reference for all purposes.